Optical cross-connect (OXC) network connectivity

[0002] The present invention relates generally to communications systems and networks, and more particularly to systems and methods for providing facility and equipment protection and restoration services in optical networks.

[0003] Modern digital telecommunications systems are built upon a hierarchical network. The network consists of a plurality of nodes or sites that are interconnected by transmission facilities. Generally, lower bandwidth level demands are multiplexed into higher bandwidth demands. For example, up to twenty-eight 1.544 Mbps DS1 channels can be multiplexed into a single 4.376 Mbps DS3 channel. Similarly, up to twelve DS3 channels can be multiplexed into a single 622.08 Mbps OC12 channel. Finally, up to sixteen OC12 channels can be multiplexed into a single 9.953 Gbps OC192 channel. Since a DS1 channel can carry up to twenty four telephone conversations, a single OC192 channel can carry over one hundred thousand telephone conversations.

[0004] A telecommunications network consists of equipment, which includes transmitters, receivers, and switches, and facilities, which includes the physical transport medium and regeneration and restoration devices. Because of the tremendous volume of calls carried on each channel, it is necessary, in the event of a facility or equipment failure, that service is not interrupted for any significant amount of time.

[0005] Typical communications networks have a mesh topology, in which there are alternative paths through the network between nodes. Accordingly, when there is a facility failure, as for example, when an optical fiber is cut, there is a separate path to which the traffic on the cut fiber can be switched. Today, when a cut occurs, traffic is rerouted at the DS3 level through other sites so that the origin and destination are again connected. Since one OC192 fiber connection includes 192 DS3 electrical connections, tremendous broadband digital cross-connect port capacity is required for restoration. Also, switching at the DS3 level is relatively slow.

[0006] Accordingly, it is an object of the present invention to provide protection and restoration services in the optical layer of an optical network.

[0007] An optical network according to the present invention includes a first optical cross-connect with a plurality of input ports and a plurality of output ports. The network includes a plurality of working channel optical transmitters, each including an optical signal output connected to an input port of the first optical cross-connect and a signal input. Each of the working channel optical transmitters is adapted to transmit an optical signal in a unique wavelength channel. The first optical cross-connect includes an optical measurement device at each of its input ports to sense a loss of signal at any of its input ports.

[0008] The network also includes a second optical cross-connect with a plurality of input ports and a plurality of output ports. The second optical cross-connect includes an optical measurement device at each of its input ports to sense a loss of signal at any of its input ports. A plurality of working channel optical receivers, each including an optical signal input, are connected to output ports of the second optical cross-connect. Each of the working channel receivers is adapted to receive an optical signal on one of the working channels.

[0009] The first and second optical cross-connects are interconnected by a primary route and a secondary route. The primary and secondary routes each include a wavelength division multiplexer and a wavelength division demultiplexer. Each wavelength division multiplexer includes plurality of optical inputs and one optical output. Each wavelength division demultiplexer includes one optical input and a plurality of optical outputs. The output of each multiplexer is connected to the input of a demultiplexer by optical fiber.

[0010] The network includes at least one protection channel optical transmitter that includes a signal input and an optical signal output, and a protection channel optical receiver including an optical signal input and a signal output. The optical signal output of the protection channel transmitter is connected to the first optical cross-connect and the optical signal input of the protection channel receiver is connected to the second optical cross-connect. The protection channel is adapted to carry signals in the event of a working channel transmitter or receiver failure.

[0011] In one embodiment of the present invention, the protection channel transmitter and receiver are connected transmit the protection channel on a unique wavelength over the secondary route. The secondary route includes amplification stations, each of which includes a regenerator dedicated to the protection channel. In the event of failure of the primary route, the signal of one of the working channels is transmitted on the protection channel and optical cross-connects are operated to switch the other working channels from the primary routee to the secondary route.

[0012] In an alternative embodiment of the present invention, the protection channel occupies a unique wave length, but the network includes means for converting the wavelength of the protection channel to the wavelength of a failed working channel transmitter. Transmitter and receiver are connected to the primary route through the first and second optical cross-connects, respectively.

[0013] The network includes a first protection switch controller associated with the first optical cross-connect, and a second protection switch controller associated with second first optical cross-connect. The first protection switch controller is in communication with the first optical cross-connect, the working channel transmitters, and the protection channel transmitter through a local area network. Similarly, the second protection switch controller is in communication with the second optical cross-connect, the working channel receivers, and the protection channel receiver through a local area network. The protection switch controllers are in communication with each other through a wide area network.

[0014] The protection switch controllers monitor the network for failures and take action to correct detected failures. For example, when an optical measurement device at an input port of the first optical cross-connect detects a loss of signal, which indicates the failure of a working channel transmitter, the first protection switch controller switches the input signal from the failed transmitter to the protection channel transmitter and notifies the second protection switch controller of the switch. When a loss of signal or an alarm indication signal is detected at the receiving end of the network, the second protection switch controller operates the second optical cross-connect to connect the working channel receivers to the secondary route and notifies the first protection switch controller to operate the first optical cross-connect to switch the working channel transmitters to the secondary route.

[0015] In the alternative embodiment of the invention, the protection switch controllers each include an optical signal input connected to an output port of its associated cross-connect and an optical signal output connected to an input port of the cross-connect. Each protection switch controller includes a frequency converter that converts optical signals between the wavelength of the protection channel and the wavelength of a failed channel.

[0016] When the first protection switch controller detects a working channel transmitter failure, the first protection switch controller switches the input signal from the failed transmitter to the protection channel transmitter and operates the first optical cross-connect to switch the output of the protection channel transmitter to the optical input of the protection switch controller. The first protection switch controller converts the wavelength of the signal to that of the failed transmitter channel and operates the first optical cross-connect to connect the output of the first protection switch controller to the primary route.

[0017] FIG. 1 is a block diagram of one embodiment of a system according to the present invention.

[0018] FIG. 2 is a block diagram of an alternative embodiment of a system according to the present invention.

[0019] Referring now to the drawings, a portion of an optical network is illustrated in FIG. 1. The network of FIG. 1 includes a first optical cross-connect 11 and a second optical cross-connect 13. Optical cross-connects 11 and 13 are interconnected by a plurality of optical transmission routes, including a primary route, designated generally by the numeral 15, and a secondary route, designated generally by the numeral 17. Routes 15 and 17 may be routed along the same path or they may be diversely routed, according to the design of the network.

[0020] The network includes a plurality N of working channel transmitters that transmit working channels W1-WN. Each working channel is transmitted on a different optical wavelength. The optical outputs of working channels W1-WN are received at optical cross-connect 11. Each optical input port of optical cross-connect 11 includes an optical measurement device 19 that is adapted to detect a loss of signal on any one of working channels W1-WN.

[0021] Optical cross-connect 11 includes a plurality of output ports. A number of output ports corresponding to the number of working channels W1-WN are connected to a wavelength division multiplexer 21. Wavelength division multiplexer 21 receives the optical signals on working channels W1-WN and multiplexes them into a single optical channel, which it outputs onto an optical fiber 23, which is part of primary route 15.

[0022] Primary route 15 includes a plurality of line amplifier stations, including a line amplification station designated generally by the numeral 25. Line amplification station 25 includes a wavelength division demultiplexer 27, which receives the optical signal from optical fiber 23 and demultiplexes it into N individual signals corresponding to working channels W1-WN. The working channels are received by a corresponding plurality N of line regenerators or repeaters LRE1-LREN. The line regenerators convert the signal from the optical domain to the electrical domain, reshape and retime the electrical signal, and retransmits the signal by converting it from the electrical domain back to the optical domain. The optical outputs of LRE1-LREN are received at a wavelength division multiplexer 29 and multiplexed into a single composite optical signal for transmission on an optical fiber 31. Those skilled in the art will recognize that an optical transmission path typically includes several line amplification stations 25. However, for purposes of illustration, only one line amplification station 25 is shown.

[0023] The optical signal on fiber 31 is received at a wavelength division demultiplexer 33 associated with second optical cross-connect 13. Wavelength division demultiplexer 33 demultiplexes the optical signal into a plurality of signals corresponding to channels W1-WN, which are received at optical input ports 35 of optical cross-connect 13. Second optical cross-connect 13 outputs working channels W1-WN to a plurality of working channel receivers, each of which includes an optical signal input and a signal output.

[0024] The network of FIG. 1 includes, in addition to the working channel transmitters associated with working channels W1-WN, a protection channel transmitter, which transmits a protection channel P1. P1 is transmitted on a unique wavelength that is different from the wavelengths of working channels W1-WN. As will be explained in detail hereinafter, in the event of an equipment or facility failure, protection channel P1 is adapted to carry the traffic of one of working channels W1-WN.

[0025] Secondary route 17 includes a wavelength division multiplexer 37 connected to optical cross-connect 11, and a wavelength division demultiplexer 39 connected to second optical cross-connect 13. Secondary route 17 also includes a plurality of line amplifier stations, including a line amplification station designated generally by the numeral 38.

[0026] Line amplification station 38 is similar to line amplification station 25 in that it includes a wavelength division demultiplexer 40, which receives the optical signal from an optical fiber 42, and a wavelength division multiplexer 44, which multiplexes individual channels onto an optical fiber 46. Line amplification station 38 includes a plurality N of regenerators; however, in the preferred embodiment, N−1 of the regenerators (LRE1-LRE(N−1)) of line amplification station 38 regenerate the signals of working channels W1-W(N−1), respectively, and one regenerator LREP regenerates the signal of protection channel P1. Thus, according to the present invention, in the event of a failure of a working channel transmitter, the traffic of that transmitter is transferred to protection channel P1 where it is carried to its destination on secondary route 17. In the event of failure along primary route 15, as for example a cut of optical fiber 23 or 31, the traffic of working channel WN is transmitted on protection channel P1 and the signals of working channels W1-W(n−1) is switched by optical cross-connect 11 from primary route 15 to secondary route 17.

[0027] The network of FIG. 1 includes a first protection switch controller 41. First protection switch controller 41 is associated with first optical cross-connect 11, the working channel transmitters, and the protection channel transmitter by means of a local area network 43. First protection switch controller 41 receives failure indications from first optical cross-connect 11 and the transmitters and sends switching instructions to the transmitters and optical cross-connect 11 over LAN 43. Similarly, a second protection switch controller 45 is associated with second optical cross-connect 13 and the receivers. Protection switch controllers 41 and 45 communicate with each other by means of a wide area network 47.

[0028] Protection switch controllers 41 and 45 provide equipment protection and facility restoration services to the network of FIG. 1. Protection switch controllers 41 and 45 receive failure indications and they include logic for operating network devices to correct the problem. For example, in the event of a transmitter failure, a loss of signal is detected at one of optical measurement devices 19 of first optical cross-connect 11. When a loss of signal is detected at one of the regenerators LRE1-LREN, the detecting regenerator transmits an alarm indication signal, which is received at one of the receivers. For example, if the transmitter associated with working channel W1 becomes inoperative, a loss of signal will be received at optical measurement device 19aand an alarm indication signal will be received at the receiver associated with working channel W1. The loss of signal will be reported to first protection switch controller 41 and the alarm indication signal will be reported to second protection switch controller 45. First protection switch controller 41 will switch the input signal for working channel W1 to protection channel P1 and signal second protection switch controller 45 that the switch has occurred.

[0029] In the event of a failure between first optical cross-connect 11 and line amplifier 25, as for example, a cut in optical fiber 23, each regenerator LRE1-LREN, will experience a loss of signal and will, in turn, transmit an alarm indication signal. The alarm indication signals will be received at each receiver for working channels W1-WN, which they will report to second protection switch controller 45. Second protection switch controller 45 will operate second optical cross-connect 13 to switch the receivers associated with working channels W1-W(N−1) from the outputs of wavelength division demultiplexer 33 to the outputs of wavelength division demultiplexer 39. Substantially simultaneously, second protection switch controller 45 will signal first protection switch controller 41 to switch the working channel WN input to the protection channel P1 transmitter and switch the outputs from the transmitters associated with working channels W1-W(N−1) from wavelength division multiplexer 21 to wavelength division multiplexer 37, thereby restoring service in the network.

[0030] Referring now to FIG. 2, a portion of an optical network according to an alternative embodiment of the present invention is illustrated. The network of FIG. 2 includes a first optical cross-connect 111 and a second optical cross-connect 113. Optical cross-connects 111 and 113 are interconnected by a plurality of optical transmission routes, including a primary route, designated generally by the numeral 115, and a secondary route, designated generally by the numeral 117.

[0031] The network includes a plurality of working channel transmitters that transmit working channels W1-WN. Each working channel is transmitted on a different optical wavelength. The optical outputs of working channels W1-WN are received at optical cross-connect 111. Each optical input port of optical cross-connect 111 includes an optical measurement device 119 that is adapted to detect a loss of signal on any one of working channels W1-WN.

[0032] Optical cross-connect 111 includes a plurality of output ports. A number of output ports corresponding to the number of working channels W1-WN are connected to a wavelength division multiplexer 121. Wavelength division multiplexer 121 receives the optical signals on working channels W1-WN and multiplexes them into a single optical channel, which it outputs onto an optical fiber 123, which is part of primary route 115.

[0033] Primary route 115 includes a plurality of line amplifier stations, including a line amplifier station designated generally by the numeral 125. Line amplifier station 125 includes a wavelength division demultiplexer 127, which receives the optical signal from optical fiber 123 and demultiplexes it into a plurality of individual signals corresponding to working channels W1-WN. The working channels are received by a corresponding plurality of line regenerators or repeaters LRE1-LREN. The line regenerators convert the signal from the optical domain to the electrical domain, reshape and retime the electrical signal, and retransmits the signal by converting it from the electrical domain back to the optical domain. The optical outputs of LRE1-LREN are received at a wavelength division multiplexer 129 and multiplexed into a single composite optical signal for transmission on an optical fiber 131. Those skilled in the art will recognize that an optical transmission path typically includes several line amplification stations 125. However, for purposes of illustration, only one line amplification station 125 is shown.

[0034] The optical signal on fiber 131 is received at a wavelength division demultiplexer 133 associated with second optical cross-connect 113. Wavelength division demultiplexer 133 demultiplexes the optical signal into a plurality of signals corresponding to channels W1-WN, which are received at optical input ports 135 of optical cross-connect 113. Second optical cross-connect 113 outputs working channels W1-WN to a plurality of working channel receivers, each of which includes an optical signal input and a signal output.

[0035] Secondary route 117 includes a wavelength division multiplexer 137 connected to optical cross-connect 111, and a wavelength division demultiplexer 139 connected to second optical cross-connect 113. Secondary route 117 also includes line amplification stations, which include regenerators LRE1-LREN but are not shown for purposes of clarity.

[0036] The network of FIG. 2 includes, in addition to the working channel transmitters associated with working channels W1-WN, a protection channel transmitter, which transmits a protection channel P1. P1 is transmitted on a unique wavelength that is different from the wavelengths of working channels W1-WN. Protection channel P1 is received at a port 119pof first optical cross-connect 111. The receivers at second optical cross-connect 113 include a protection channel receiver, which is adapted to receive protection channel P1 from second optical cross-connect 113. It will be noted in FIG. 2 that the optical signal of protection channel P1 goes through optical cross-connects 111 or 113, rather than directly into and out of primary route 115 directly through wavelength division multiplexer 121 and wavelength division demultiplexer 133, as in the embodiment of FIG. 1. It will be further noted that line amplification station 125 of FIG. 2 does not include a separate line regenerator for protection channel P1. Rather, line amplification station 125 includes only as many line regenerators LRE1-LREN as there are working channels W1-WN.

[0037] The network of FIG. 2 includes a first protection switch controller 141. First protection switch controller 141 is associated with first optical cross-connect 111, the working channel transmitters, and the protection channel transmitter by means of a local area network 143. First protection switch controller 141 receives failure indications from first optical cross-connect 111 and the transmitters and sends switching instructions to the transmitters and optical cross-connect 111 over LAN 143. Similarly, a second protection switch controller 145 is associated with second optical cross-connect 113 and the receivers. Protection switch controllers 141 and 145 communicate with each other by means of a wide area network 147.

[0038] Each protection switch controller 141 and 145 includes optical frequency conversion means, which are not shown but are generally well known to those skilled in the art. First protection switch controller 141 has means for converting an optical signal in the wavelength protection channel P1 to an optical signal in the wavelength of a selected one of working channels W1-WN. Similarly, second protection switch controller 145 has means for converting an optical signal in the wavelength of working channels W1-WN to an optical signal in the wavelength of protection channel P1.

[0039] First protection switch controller 141 has an optical input connected to an output port of first optical cross-connect 111, and an optical output connected to an input port 119sof first optical cross-connect 111. Similarly, second protection switch controller 145 has an optical input connected to an output port of second optical cross-connect 113, and an optical output connected to an input port 135sof second optical cross-connect 113.

[0040] Protection switch controllers 141 and 145 provide equipment protection and facility restoration services to the network of FIG. 2. Protection switch controllers 141 and 145 receive failure indications and they include logic for operating network devices to correct the problem. For example, in the event of a transmitter failure, a loss of signal is detected at one of optical measurement devices 119a-119nof first optical cross-connect 111. When a loss of signal is detected at one of the regenerators LRE1-LREN, the detecting regenerator transmits an alarm indication signal, which is received at one of the receivers. For example, if the transmitter associated with working channel W1 becomes inoperative, a loss of signal will be received at optical measurement device 119aand an alarm indication signal will be received at the receiver associated with working channel W1. The loss of signal will be reported to first protection switch controller 141 and the alarm indication signal will be reported to second protection switch controller 145. First protection switch controller 141 will switch the input signal for working channel W1 to protection channel P1. First protection switch controller 141 will operate first optical cross-connect 111 connect P1 to first protection switch controller 141, which will convert the wavelength of the P1 signal to the wavelength of the W1 channel. Additionally, first protection switch controller 141 will operate first optical cross-connect 111 connect input port 119sto wave division multiplexer 121. The protection channel signal will be received at the working channel W1 receiver in the normal way.

[0041] In the event of a failure between first optical cross-connect 111 and line amplifier 125, as for example, a cut in optical fiber 123, each regenerator LRE1-LREN, will experience a loss of signal and will, in turn, transmit an alarm indication signal. The alarm indication signals will be received at each receiver for working channels W1-WN, which they will report to second protection switch controller 145. Second protection switch controller 145 will operate second optical cross-connect 113 to switch the receivers associated with working channels W1-WN from the outputs of wavelength division demultiplexer 133 to the outputs of wavelength division demultiplexer 139. Substantially simultaneously, second protection switch controller 145 will signal first protection switch controller 141 to switch the outputs from the transmitters associated with working channels W1-WN from wavelength division multiplexer 121 to wavelength division multiplexer 137, thereby restoring service in the network.

[0042] Similarly, if a failure occurs between line amplifier 125 and second optical cross-connect 113, a loss of signal will be reported at each optical measurement device 135a-135n. Again, protection switch controllers 141 and 145 will operate optical cross-connects 111 and 113, respectively, to switch working channels W1-WN from primary route 115 to secondary route 117.